Systems carried onboard aircraft for detecting turbulence in advance and thus avoiding deleterious consequences to the aircraft or to its occupants are known.
Turbulence is manifested as sudden local variations in wind velocity and direction, which are the cause of haphazard and uncontrolled movements of airplanes. Indeed, the movements of air with respect to the ground, or, stated otherwise, with respect to the Terrestrial reference frame, that are also referred to as the wind, are not homogeneous. In particular, spatial wind heterogeneities create increments of angle of attack or sideslip which generate movements of the airplane.
The avoidance by the aircraft of a risk zone assumes identification and location of a turbulence zone with sufficient notice to re-schedule the trajectory of the aircraft, with agreement of the air traffic control, i.e. typically 5 minutes at the minimum.
Entry into such a risk zone requires flight control actions in preparation for crossing the zone.
Among these consequences, the most frequent relates to bodily accidents involving persons aboard the aircraft. These accidents may be caused by abrupt unexpected accelerations or rotations of the aircraft when it crosses a zone of turbulence. These accelerations may give rise, on the one hand, to impacts between persons and the walls of the aircraft, for example against the ceiling of the passenger cabin when the persons are not strapped into their seat, and on the other hand, the striking of persons by objects that are not securely fixed to the structure of the aircraft, for example service trolleys. The cost of these accidents is high.
Much more rarely, the crossing of a zone of turbulence by an aircraft may damage its structure, notably when intense winds are present in the zone of turbulence.
The vertically directed wind components have an influence on the angle of attack, therefore on the lift of the aircraft, and the laterally directed components have a yaw influence on the aircraft through the changes in sideslip on the tailfin.
The detection of these wind heterogeneities can make it possible either to prepare the aircraft to confront these difficulties by taking rapid actions, or to trigger an avoidance maneuver so as to sidestep the danger zone.